Source : Webster's Revised Unabridged Dictionary (1913)

Chromogen \Chro"mo*gen\, [Gr. ? color + -gen.]
   1. (Biol.) Vegetable coloring matter other than green;
      chromule.

   2. (Chem.) Any colored compound, supposed to contain one or
      more chromophores.

Source : WordNet®

chromogen
     n : a compound that can be converted to a pigment